Question

I have an asset manager that needs to notify the owner it’s assets are ready. I’m sending a token back for the consumer to listen to listen for a notification to avoid tighter coupling. The issue is when the assets are already loaded I need to call the loadComplete after a delay. What’s the best way to do this in objective-c?

Asset Manager

-(tokenString*) loadAssetPath:(NSString*) asset {
    //start asynchronous load
    //or if assets ready send complete       <-- issue
    return nonceToken;
}
-(void)loadComplete {
    [[NSNotificationCenter defaultCenter] 
        postNotificationName:tokenString object:self];
}

Consumer

NSString* token;
-(void) loadSomething {
    if(token)
        [self removeListener];
    token = [[AssetManager sharedManager] 
        loadAssetPath:@"http://server.dev/myLargeImage.png"];
    [[NSNotificationCenter defaultCenter] 
        addObserver:[AssetManager sharedManager] 
        selector:@selector(assetLoaded:) name:token];
}
-(void)assetLoader:(NSNotifcation*)aNotification {
    [self removeListener];
    //continue on with stuffing stuff
}

Answer 1

Use NSObject’s performSelector function which allows it to be called after a delay.

- (void)performSelector:(SEL)aSelector withObject:(id)anArgument afterDelay:(NSTimeInterval)delay

You can even use a form of this function to run it on another thread, which is useful to not blocking the main thread when doing lengthy operations (just don’t muck with the UI objects in this thread).